Multibeam particle microscope with improved beam current control

Abstract

A multi-beam particle microscope with improved beam current control is disclosed. Excess electrons discharged from one or only a few regions of an absorber layer provided on a multi-aperture array are measured using an ammeter. The measured current is used as a controlled variable in a closed-loop control. The measurement is large-area and low-noise. The multi-aperture array can be specially structured to also provide direction-sensitive detection, for example using a quadrant or tripartite detector.

Description

[Technical field]

[0001] Generally, the present invention relates to a multi-beam particle microscope that operates using multiple individual particle beams, and more particularly, to a multi-beam particle microscope with improved beam current control. [Background technology]

[0002] With the continuous development of increasingly smaller and more complex microstructures, such as semiconductor components, there is a need to develop and optimize planar manufacturing techniques for producing the microstructures and inspection systems for inspecting the critical dimensions. For example, the development and manufacturing of semiconductor components requires the monitoring of the design of test wafers, and planar manufacturing techniques require process optimization for reliable manufacturing with high throughput. Also, there is a recent demand for the analysis of semiconductor wafers for reverse engineering and for customer-specific individual configuration of semiconductor components. Therefore, there is a need for inspection means that can be used with high throughput to examine the microstructures on the wafer with high accuracy.

[0003] Typical silicon wafers used in the manufacture of semiconductor components have a diameter of up to 300 mm. Each wafer can be up to 800 mm 2A semiconductor device includes a plurality of semiconductor structures, which are fabricated in layers on the surface of a wafer by planar integration techniques. The semiconductor wafer typically has a flat surface resulting from the fabrication process. In this case, the structure size of the integrated semiconductor structures ranges from a few microns to a critical dimension (CD) of 5 nm, but the structure dimensions will become smaller in the near future. In the future, the structure size or critical dimension (CD) is expected to be less than 3 nm, e.g., 2 nm, or even less than 1 nm. For the above small structure sizes, defects of the size of the critical dimension need to be identified quickly over a very large area. For some applications, the specification requirements for the accuracy of the measurements provided by the inspection device are, for example, two or even one order of magnitude higher. For example, the width of the semiconductor features needs to be measured with an accuracy of less than 1 nm, e.g., 0.3 nm or even finer, and the relative positions of the semiconductor structures need to be determined with an overlay accuracy of less than 1 nm, e.g., 0.3 nm or even finer.

[0004] The MSEM or multi-beam scanning electron microscope is the result of relatively recent advances in the field of charged particle systems (charged particle microscopes (CPM)). For example, multi-beam scanning electron microscopes are disclosed in US Patent Publication No. 7244949B2 and US Patent Application Publication No. 2019 / 0355544. In the case of a multi-beam electron microscope or MSEM, a sample is simultaneously irradiated with a number of individual electron beams arranged in a field or raster. For example, 4-10000 individual electron beams can be provided as primary irradiation, each individual electron beam being spaced apart from the adjacent individual electron beams by a pitch of 1-200 micrometers. For example, an MSEM has about 100 separate individual electron beams ("beamlets"), which are arranged, for example, in a hexagonal raster, the individual electron beams being spaced apart by a distance of about 10 μm. A number of charged individual particle beams (primary beams) are individually focused on the surface of the sample to be examined, each time by means of a common wide-field optical system, in particular a common objective lens. For example, the sample can be a semiconductor wafer fixed on a wafer holder assembled on a movable stage. During irradiation of the wafer surface by the charged primary individual particle beam, interaction products, e.g. secondary electrons or backscattered electrons, emerge from the surface of the wafer. Their respective starting points correspond to locations on the sample on which the multiple primary individual particle beams are focused in each case. The amount and energy of the interaction products depend, inter alia, on the material composition and the topography of the wafer surface. The interaction products form multiple secondary individual particle beams (secondary beams), which are collected by a common objective lens and, as a result of a projection imaging system of the multi-beam inspection system, impinge on a detector arranged in a detection plane. The detector comprises multiple detection areas, each of which comprises multiple detection pixels, and the detector captures the respective intensity distribution of the secondary individual particle beams. In this process, an image field of, e.g., 100 μm×100 μm is obtained.

[0005] Prior art multi-beam electron microscopes include a series of electrostatic and magnetic elements. At least some of the electrostatic and magnetic elements are adjusted to adapt the focal position and astigmatism of the multiple charged individual particle beams. Prior art charged particle multi-beam systems further include at least one crossover plane of the primary or secondary charged individual particle beams. Prior art systems also include a detection system to make the adjustment easier. Prior art multi-beam particle microscopes include at least one beam deflector ("deflection scanner") for sweeping an area of ​​the sample surface with multiple primary individual beams to obtain an image field of the sample surface. Further details regarding the multi-beam electron microscope and a method for operating it are described in the German patent application with application number 102020206739.2, filed on May 28, 2020, the disclosure of which is incorporated in its entirety by reference into this patent application.

[0006] As the requirements for imaging quality increase, so do the requirements for the multi-beam particle microscope used for imaging. To obtain high-quality recordings, stable operating parameters are crucial. One of these is the beam current intensity of the individual particle beams used to scan the sample surface.

[0007] For a uniform beam current intensity of the individual particle beams, the radiation characteristics of the particle beam source, more precisely the uniformity of the radiation characteristics over the entire used radiation angle, is important. When using a relatively large radiation angle, the radiation characteristics of the particle source, for example a thermal field emission (TFE) source, are not uniform throughout. Therefore, the irradiance at the first multi-aperture plate in the corresponding particle beam system is also not uniform throughout, and there are relatively large variations in the current density in the different individual beams. However, in the case of a multi-particle inspection system, it is a system requirement that there is only a small variation in the current intensity between the various individual beams, typically less than a few percent, or even less than one percent, so that all individual image fields of a multi-image field are scanned with an equal number of particles or electrons. For example, this is a prerequisite for obtaining individual images with approximately the same brightness. The obtained resolution of the individual images also depends on the individual beam currents.

[0008] There are several options for individual adjustment of the beam current of the individual particle beams, one option in this regard is disclosed in DE 10 2018 007 652 A1, the disclosure of which is incorporated in its entirety into the present patent application by reference.

[0009] The emission characteristics of the particle source may also change gradually over time and generally exhibit a drift behavior. The particle source or tip may age and may, for example, decrease in brightness. The brightness of the image is further correlated with the brightness or luminance of the particle source. If the brightness of the particle source decreases, this also applies to the brightness of the image. Also, for example, the particle beam initially emitted from the particle source may change its direction. It is therefore desirable to take measures that allow to provide a more stable and uniform beam current when scanning a sample with multiple individual charged particle beams or beamlets.

[0010] This means, among other things, that the requirements for a stable beam current become even higher. Usually, the beam current stability of a multibeam particle microscope was considered sufficiently stable if the relative fluctuation of the beam current with respect to a reference beam current was ≦10% or ≦5% over an hour. For future measurement tasks, such a stability is no longer considered sufficient. Higher requirements have to be met: the relative beam current fluctuation with respect to a reference beam current of a multibeam charged particle microscope must be less than or equal to 1% over at least a month.

[0011] The state of the art discloses several principles for measuring or monitoring the beam current and for controlling it, respectively, but with regard to higher requirements of beam current stability it has been found that the already existing solutions are not sufficient and need to be improved.

[0012] US Patent Application Publication No. 2020 / 0312619 discloses a system and method for measuring beam current in a multi-beam device, which may be a multi-beam particle microscope. The multi-beam particle microscope includes a charged particle beam source configured to generate a primary charged particle beam and a multi-aperture array. The multi-aperture array includes a plurality of apertures configured to form a plurality of beamlets from the primary charged particle beam, and a detector including a circuit for detecting the current of at least a portion of the primary charged particle beam illuminating the multi-aperture array. More specifically, a plurality of miniature detectors with circuitry are provided in tiny additional holes provided on the upper side of the multi-aperture array. These holes are associated with specific apertures, are therefore tiny, and are provided in the vicinity of the specific apertures. These holes are provided in the array of apertures, directly at the border of the array and in contact with the theoretical circumferential area of ​​the array. Examples of detectors with circuitry are Faraday cups, diodes, arrays of diodes, scintillators, or photomultipliers. A detector with circuitry is used to monitor the current incident on the detector, and the total current can be determined from the measurements. It is also possible to detect changes in the current, such as the beam position, the beam diameter, the beam current itself, the beam current density, and the uniformity of the beam current density. These changes can be corrected by controlling the extraction voltage, the acceleration voltage, the beam deflection voltage, etc.

[0013] US2020 / 0312619 has several drawbacks: the overall sensitivity of the beam current detection is limited due to the small area used for a single detection. Assuming that the detector surface area is comparable to the area of ​​the aperture generating the beamlets, the beam current measured at the detector is of the same order of magnitude as the single beam current passing through the associated aperture. Typically, this single beam current is of the rather low order of a few hundred picoamperes. Therefore, it is even more difficult to detect variations significantly smaller than 1%, and the signal-to-noise ratio of detectors with such a small entrance surface is relatively high. Also, the boundaries of the detectors integrated within the holes of the multi-aperture plate can create problems due to cumulative changes that can adversely affect the beam direction and beam quality of the beamlets. Furthermore, the manufacture of small detectors is complex. Overall, therefore, the detection system according to US2020 / 0312619 is not suitable for measurement tasks that require beam current stability better than 1% over a period of one month or even longer.

[0014] US Patent No. 6,969,862 B2 discloses a beam current detector for a lithography system. The patent discloses a multi-beam device including a charged particle source configured to generate a primary charged particle beam and an aperture array. The aperture array includes a number of apertures configured to form a number of beamlets from the primary charged particle beam and a detector coupled to a circuit and configured to detect the current of at least a portion of the primary charged particle beam illuminating the aperture array, the detector being located on the beam exit side of the aperture array relative to the primary charged particle beam. The multi-beam device according to US Patent No. 6,969,862 B2 is therefore very similar to the multi-beam device according to US Patent Application Publication No. 2020 / 0312619 cited above. The difference between both these publications is that the detector is located on the beam entrance side according to US Patent Application Publication No. 2020 / 0312619, but on the beam exit side according to US Patent No. 6,969,862 B2. However, the measurement principle is the same in both cases, since the detected beam current in both cases enters a specially provided hole at the beam entrance side of the multi-aperture array and is then directly detected by a detector equipped with a circuit. Therefore, the detection system according to US Pat. No. 6,969,862 B2 is also not suitable for measurement tasks requiring beam current stability better than 1% over a period of one month or even longer.

[0015] US Patent No. 7,388,214 B2 discloses a charged particle beam exposure apparatus that splits a charged particle beam from a charged particle beam source into multiple charged particle beams by multiple apertures formed in an aperture array to expose a wafer using multiple charged particle beams. The apparatus includes a stage for mounting a wafer on which the multiple charged particle beams passing through the apertures of the aperture array are irradiated, multiple detection electrodes for detecting the intensity of the multiple charged particle beams passing through the multiple apertures of the aperture array to expose the wafer to the multiple charged particle beams, the detection electrodes being formed on the charged particle beam source side in the light-shielding peripheral areas of the multiple apertures of the aperture array, and a grid array (including a grid electrode) for adjusting the intensity of the multiple charged particle beams based on the detection results obtained by the multiple detection electrodes. The detection system according to US Patent No. 7,388,214 B2 is also not suitable for measurement tasks that require beam current stability better than 1% over a period of one month or even longer. Since the detection electrodes provided on the electrode pads are preferably each assigned to one aperture, the detection area is again very small and therefore the signal-to-noise ratio of the beam current measurement is relatively small. The assignment of several detection electrodes to one pad is also disclosed and is taught to improve the detection accuracy. However, on the other hand, this assignment has the disadvantage that the accuracy of the specific control using the grid electrodes is reduced, since the same control voltage is applied to the grid electrodes as a result of the common wiring of the pads. The area used for detection therefore has to remain small overall at the expense. There is also a risk that any active influence on the beamlets using charges on the multi-aperture array will further affect the beamlet quality. From a manufacturing point of view, US Pat. No. 7,388,214 B2 is also rather complex.

[0016] US Patent No. 9,607,806 B2 discloses a multi-beam lithography system having a detector for beam control located at a specific position above the multi-aperture array, which is capable of measuring the beam current when the beam is deflected or blanked.

[0017] US Patent No. 6,617,587 B2 discloses a multi-beam lithography system that has a tip conditioning circuit that is part of the electrode gun itself and has separate current collection areas on a single aperture plate for each of the multiple beams.

[0018] US Patent No. 5,111,053A discloses the control of a liquid metal ion source with analog feedback and digital CPU control. This document relates to a single beam system. A monitoring electrode is applied to measure the beam current and the extraction voltage of the particle source is adjusted.

[0019] US Patent No. 7,091,486 B1 first describes a conventional technique for correcting beam current fluctuations in a single beam system. The conventional technique for correcting beam current fluctuations described uses a circuit connected to a beam stop aperture to measure the current from the aperture. This current is due to electrons being absorbed by the aperture. From the measured current, the beam current can be estimated. Changes in the measured current are used to estimate changes in the beam current. This conventional technique is taught to be suitable for detecting fluctuations only within a limited frequency bandwidth. In particular, it is said that detecting high frequency (e.g., above a few kilohertz) fluctuations is problematic. This bandwidth limitation is said to be due to the low current levels and high stray capacitance in this conventional technique. Therefore, US Patent No. 7,091,486 B1 teaches the use of a high speed detector mounted above the aperture to collect and measure secondary and / or backscattered electrons. The secondary and / or backscattered electrons are emitted due to the impact of a portion of the primary beam (the portion that is blocked) against the aperture. Fast electronic detectors include, for example, Everhart-Thornley detectors, PIN diode-based detectors, and microchannel plate detectors. Summary of the Invention

[0020] It is therefore an object of the present invention to provide a multi-beam particle microscope with improved beam current stability, which will be suitable for measurement tasks requiring beam current stability better than 1% over periods of one month or even longer, and mechanisms for implementing the respective feedback control which will be easy to manufacture and implement.

[0021] This object is achieved by the subject matter of the independent claims. Advantageous embodiments of the invention emerge from the dependent claims.

[0022] This patent application claims priority to German patent application No. 102021118561.0, filed on July 19, 2021, the disclosure of which is incorporated by reference in its entirety into this patent application.

[0023] According to a first aspect of the invention, there is provided a multi-beam particle microscope comprising: a beam generating system including a particle source, an extractor electrode, and an anode, the beam generating system being configured to generate a first charged particle beam; a multi-beam generator having a multi-aperture array configured to generate a first field of a plurality of first individual charged particle beams from a first charged particle beam, the multi-aperture array including an absorber layer thereon for absorbing the charged particles, the absorber layer being connected to at least one ground electrode for discharging excess electrons; a first beam current measuring means configured to measure at least discharged excess electrons generated by charged particles impinging on the multi-aperture array over a large area in an outer region around all of the openings in the multi-aperture array; a condenser lens system disposed between the beam generating system and the multi-beam generator; a first particle-optical unit having a first particle-optical beam path configured to direct the generated first individual particle beam towards the sample such that the first individual particle beam strikes the sample at incidence locations that form a second field of view; A detection system; a second particle-optical unit having a second particle-optical beam path configured to image a second individual particle beam emanating from an incidence position within the second field of view onto the detection system; a particle optical objective lens through which both the first and second individual particle beams pass; a beam switch disposed in the first particle-optical beam path between the multi-beam generator and the objective lens and disposed in the second particle-optical beam path between the objective lens and the detection system; a controller configured to control the beam generation system, the focusing lens system, the particle-optical objective, the first particle-optical unit, the second particle-optical unit, and the detection system; a controller configured to control the beam generating system based on the measurement using the first beam current measurement means; and / or The present invention relates to a multi-beam particle microscope, wherein the controller is configured to control the focusing lens system based on measurements using the first beam current measuring means.

[0024] The individual charged particle beams may be, for example, electrons, positrons, muons or ions, or other charged particles.

[0025] The multi-aperture array is preferably an array arranged as a first multi-aperture array downstream of a collecting lens system in the particle-optical beam path of the multi-beam particle microscope. This multi-aperture array is preferably an array that splits the first charged particle beam into a plurality of individual charged particle beams. In this case, the multi-aperture array is preferably a component of what is called a micro-optical system, which preferably consists of or includes a series of a plurality of multi-aperture plates or multi-aperture arrays (the two expressions are used synonymously within this patent application). In this context, for good image quality, the first charged particle beam emanating from the particle source or tip must be uniformly incident on the multi-aperture array, in particular as vertically as possible, and must also illuminate the multi-aperture array as uniformly or centrally as possible. It is then possible to ensure that the beam current of the individual particle beams passing through the multi-aperture array is sufficiently uniform in the individual particle beams. Uniform illumination can be achieved not only in the case of telecentric incidence of the first charged particle beam on the multi-aperture array, but also in the case of divergent or convergent incidence, and in any case where the central beam axis is aligned perpendicular to the surface of the multi-aperture array. Here, the openings in the multi-aperture array are preferably circular, but may have other shapes. Preferably, the openings in the multi-aperture array have a regular arrangement, for example a rectangular, square or hexagonal arrangement. In the case of a hexagonal arrangement, preferably 3n(n-1)+1 openings are provided, where n is any natural number.

[0026] The multi-aperture array or multi-aperture plate comprises on its upper side an absorbing layer capable of absorbing electrons. Preferably, the absorbing layer is provided on substantially the entire surface of the multi-aperture array (except of course the apertures), and thus not only in the inner area including the apertures, but also in the outer area around all of the openings in the multi-aperture array. Also existing multi-beam particle microscopes of the state of the art are provided with such an absorbing layer. This ensures that no charge accumulates on the surface of the multi-aperture array, which would significantly degrade the beam quality of the first individual particle beam.

[0027] The measurement system can be calibrated based on an individual particle beam being measured, for example, using a moveable stage and, for example, a Faraday cup thereon.Other embodiment variations and calibration methods are also contemplated.

[0028] According to the invention, a first beam current measurement means is provided, which is configured to measure at least discharge excess electrons generated by charged particles impinging on the multi-aperture array in an outer region around all of the apertures in the multi-aperture array over a large area. Unlike the current state of the art for multi-beam particle devices, the measurement is performed over a large area and not in a small area typically used when separate detectors are placed on the multi-aperture array. The enlarged area significantly improves the signal-to-noise ratio during detection. Also, surprisingly, the inventors' measurements have found that any fluctuations in the signal obtained by the measurement over a large area in the outer region around all of the apertures in the multi-aperture array reflect the beam current fluctuations of the individual particle beams. Thus, the measurement over a large area is not an averaging that covers larger fluctuations in the beam current of the individual charged particle beams. This discovery is extremely important and is a conceptual change to the current state of the art, where the main focus is on measuring the beam current as precisely as possible for each individual particle beam separately. Surprisingly, such separate measurements for each individual particle beam are not necessary.

[0029] Moreover, the first beam current measuring means according to the invention does not require a separate detection device that needs to be integrated on the multi-aperture array, and therefore does not require a specific circuit. The solution according to the invention is therefore very simple, and therefore makes the multi-aperture array very easy to manufacture. Any detection device, typically an ammeter, in particular a picoammeter, can be provided at a distance from the multi-aperture array. It is not necessary to provide an ammeter in the vacuum provided inside the multi-beam particle microscope, but the ammeter can be provided outside the vacuum.

[0030] The measurement principle is also different from that applied in multi-beam devices according to the state of the art. According to the state of the art, the particles measured by a detector separately provided on the multi-aperture array are those that impinge on the multi-aperture array, or more precisely at the location where the detector is provided. In contrast, according to the invention, the excess electrons that are measured are not at least directly impinging charged electrons, but can be transported and "converted", and are nevertheless a measure of the impinging charged particles. This becomes evident when the multi-beam particle microscope works with ions and not with electrons. The ions are too large to be absorbed in the absorbing layer, but still stick to the surface of the absorbing layer. The ions release electrons, which can be transported and discharged, or discharge an equivalent number of existing electrons.

[0031] According to the present invention, discharge excess electrons generated by charged particles impinging on the multi-aperture array in the outer region around all of the apertures in the multi-aperture array are measured over a larger area. The entire outer region around the apertures provides such a large area. Part of the outer region can also provide a large area, thus achieving an improved signal-to-noise ratio for detection. Also, the measurement based on the impinging particles in the outer region can indicate a position shift of the entire beam cone of the first charged particle beam.

[0032] According to an embodiment, the first beam current measuring means is also configured to measure discharge excess electrons generated by charged particles impinging on the multi-aperture array in an inner region including the openings in the multi-aperture array. The measurement of excess electrons originating from the inner region and from the outer region can be performed as a global excess electron measurement by one ammeter. In this case, the interaction area for the measurement is maximized and the signal-to-noise ratio is the best. However, in this case, the position deviation of the entire first charged particle beam cannot be detected separately. However, this embodiment is the easiest to implement in existing systems.

[0033] The first beam current measuring means according to the invention can in this case be implemented as a control loop, which in principle is already known from the state of the art. The controller can be configured for example to control the beam generating system based on the measurement with the first beam current measuring means. Additionally or alternatively, the controller can be configured for controlling the focusing lens system based on the measurement with the first beam current measuring means. Other types of control embodiments are also possible. The beam current measuring means can be calibrated, for example, based on an individual particle beam measured using a movable stage and, for example, a Faraday cup thereon. Other embodiment variants and calibration methods are also conceivable.

[0034] According to an embodiment, the absorber layer on the multi-aperture array is structured in exactly two separate regions separated from each other, each region connected to ground, the first region being an inner region including the openings of the multi-aperture array and the second region being an outer region all around the openings in the multi-aperture array, the first beam current measuring means being configured to measure only the excess electrons discharged from the outer region. Preferably, the inner region and the outer region are complementary regions on the multi-aperture array. In other words, the entire surface of the multi-aperture array consists of the inner region and the outer region. The measurement of the excess electrons discharged from the outer region is sufficient to measure and thus control the fluctuations in the beam current of the individual charged particle beams. The inner region is not at all disturbed by any measurement or any structuring of the absorber layer, and thus the beam quality of the individual particle beams can be maintained in its best state.

[0035] According to one embodiment, the absorber layer on the multi-aperture array is structured into at least two separate regions separated from each other, each region connected to ground, and the first beam current measuring means is configured to measure the excess electrons discharged separately from each region over a large area. The structuring of the absorber layer is therefore limited to such a division that still results in sufficiently large separate regions. This is necessary to ensure a good signal-to-noise ratio of the measurement. According to a preferred embodiment, the entire structuring divides the absorber layer into up to five or six separate regions.

[0036] According to an embodiment, the absorber layer is structured in an inner region including the openings of the multi-aperture array and in an outer region all around the openings in the multi-aperture array. The outer region is further structured in four separate regions arranged to form a direction indicating quadrant detector, the first beam current measuring means being configured to measure over a large area the excess electrons discharged separately from each quadrant. Preferably, the inner region is completely unstructured and left intact. The excess electrons discharged from the inner region can be optionally measured. The term quadrant detector denotes the whole arrangement of separate regions suitable for indicating the direction of movement of the beam cone impinging on the multi-aperture array. The size of each quadrant is preferably chosen to be approximately the same, although certain deviations may be advantageous depending on the specific arrangement of the openings in the multi-aperture plate resulting in a specific geometry of the envelope around the openings. This envelope can define the boundary between the inner and outer regions and can be used for structuring and separation.

[0037] According to another embodiment, the absorber layer is structured in an inner region and an outer region, the outer region being further structured in three separate regions to form a direction indicating tertiary detector, the first beam current measuring means being configured to measure the excess electrons discharged from each of the three separate regions separately. The arrangement of the three separate regions of the tertiary detector derives from a triangular arrangement of the separate detection regions. After a calibration process, any deviation detected with one of the three separate regions may indeed indicate a position deviation, in principle allowing an analysis of the type of position deviation. The use of a direction indicating tertiary detector is advantageous in that the number of structures / separations of the regions is further limited, thus further minimizing the influence of the accumulated charge on the surface of the multi-aperture array on the beam current quality. The inner region is preferably not structured at all and is left completely untouched. The excess electrons discharged from the inner region can be optionally measured.

[0038] According to a preferred embodiment of the invention, the multi-beam particle microscope further comprises a double deflector in the region of the collecting lens system, the controller of the multi-beam particle microscope being further configured to control the double deflector on the basis of measurements using the beam current measuring means. The double deflector is preferably an electrostatic double deflector, which can be operated faster compared to a magnetic double deflector. However, a magnetic double deflector is also feasible. The double deflector can shift the entire first charged particle beam in parallel and thus correct position deviations of the beam cone impinging on the multi-aperture array.

[0039] In principle, the first beam current measuring means can comprise one or more components. According to a very clear and simple embodiment, the first beam current measuring means comprises only one component. In the case of several components, the components are preferably identical, but may also be different from each other.

[0040] According to a preferred embodiment, the first beam current measuring means comprises at least one ammeter, in particular a picoammeter, which is extremely sensitive and can detect already very small fluctuations of the provided excess electrons, which are a measure of the beam current.

[0041] According to a preferred embodiment, at least 60% of the beam current reaching the multi-aperture array is used for the beam current measurement, which ensures a good signal-to-noise ratio since a large area is measured.

[0042] According to a preferred embodiment, at least 90%, preferably at least 95%, of the beam current reaching the multi-aperture array is used for the beam current measurement. The above values ​​are typically achieved when the entire surface of the multi-aperture array is provided with an absorbing layer and all the discharged excess electrons transported to the ground electrode are measured. This can be done using one measuring device, such as a picoammeter, or using several measuring devices, for example several picoammeters.

[0043] According to an embodiment, the active beam measurement surface of the absorbing layer, which absorbs the charged particles and discharges electrons therefrom for beam current measurement, is at least 60% of the total surface of the multi-aperture array. Preferably, the active beam measurement surface is at least 90%, even more preferably 95%, of the total surface of the multi-aperture array. There is a difference between referring to the active beam measurement surface and referring to the beam current reaching the multi-aperture array. The active beam measurement surface is fixed by design, for example by providing an absorbing layer and a connection to ground, for example via an ammeter. In contrast, the proportion of the beam current reaching the multi-aperture array depends on the operating settings of the multi-beam particle microscope, for example on the set beam diameter of the first charged particle beam. In any case, the above preferred embodiment ensures that the measurement with the first beam current measurement means is performed over a large area, thus ensuring a good signal-to-noise ratio.

[0044] According to a preferred embodiment, the average single beam current of the plurality of first individual particle beams is 1 / 100 or less of the total beam current measured by the first beam current measuring means, preferably the average single beam current of the plurality of first individual particle beams is 1 / 500 or less, even more preferably 1 / 1000 or less of the total beam current measured by the first beam current measuring means. The generated signal is therefore much larger than the single beam current, which contributes to the required very good signal-to-noise ratio. By way of example, a typical single beam current is in the order of hundreds of picoamperes, for example 500 or 600 or 700 picoamperes. The total beam current measured with the excess charge is, for example, in the range of 500, 600 or 700 nanoamperes. However, the single beam current and the total current generated by the measured excess electrons can be larger or smaller, for example only tens of picoamperes for the single beam current and only tens of nanoamperes for the excess electrons. However, larger single beam currents up to a few nanoamperes are also possible, and even beam currents of a few microamperes measured with excess electrons.

[0045] According to one embodiment, the absorbing layer is an absorbent coating and / or comprises or consists of any one of gold, silver, titanium, platinum, which are good conductors and do not oxidize easily. In principle, noble metals are preferred.

[0046] According to an embodiment, the multi-aperture array is arranged as a first multi-aperture array downstream of the focusing lens system and is an array that splits the first charged particle beam into a plurality of first charged particle beams. Alternatively, the multi-aperture array is not arranged as a first multi-aperture array downstream of the focusing lens system. This variant can typically occur when a series of aperture plates, in particular a series of multi-aperture arrays, are provided.

[0047] According to one embodiment, the controller is configured to control the beam generating device by setting the voltage supplied to the extractor electrode, this type of control being in principle already known from the art.

[0048] According to an embodiment, the controller is configured to control the beam generating device by setting the temperature of the particle source, in particular by setting the heating current or voltage. Although this type of control is slightly slower than setting the voltage supplied to the extractor electrode, for example, it has been found to be sufficient and, moreover, easy to implement reliably during switch-on and switch-off procedures.

[0049] According to a second aspect of the invention, there is provided a multibeam particle microscope comprising: a beam generating system configured to generate a first charged particle beam, the beam generating system including a particle source, an extractor electrode, and an anode; a multi-beam generator having a pre-aperture plate and a multi-aperture array configured to generate a first field of a plurality of first individual charged particle beams from a first charged particle beam, the multi-aperture array being disposed downstream of and proximate to the pre-aperture plate, the multi-aperture array including an absorption layer on its upper side for absorbing the charged particles, the absorption layer being connected to at least one ground electrode for discharging excess electrons, the pre-aperture plate including a pre-aperture plate absorption layer on its upper side for absorbing the charged particles, the pre-aperture plate absorption layer being connected to at least one ground electrode for discharging excess electrons; a first beam current measuring means configured to measure at least discharge excess electrons generated by charged particles impinging on the pre-aperture plate; a focusing lens system disposed between the beam generating system and the multi-beam generator; a first particle-optical unit having a first particle-optical beam path configured to direct the generated first individual particle beam towards the sample such that the first individual particle beam strikes the sample at an incidence position forming a second field of view; A detection system; a second particle-optical unit having a second particle-optical beam path configured to image a second individual particle beam emanating from an incidence position within the second field of view onto the detection system; a particle-optical objective lens through which both the first and second individual particle beams pass; a beam switch disposed in the first particle-optical beam path between the multi-beam particle source and the objective lens and disposed in the second particle-optical beam path between the objective lens and the detection system; a controller configured to control the beam generation system, the particle-optical objective, the first particle-optical unit, the second particle-optical unit, and the detection system; a controller configured to drive the beam generating system based on the measurement using the first beam current measuring means; and / or The present invention relates to a multi-beam particle microscope, wherein the controller is configured to control the focusing lens system based on measurements using a first beam current measuring means.

[0050] As already mentioned above, the multi-beam generator can include a series of aperture plates and multi-aperture plates, which can be part of a so-called micro-optical system. One feature according to the invention according to the first aspect is that excess electrons generated by impinging particles in the outer region of the multi-aperture array are used for the beam current measurement. Of course, it is also possible to arrange a pre-aperture plate, meaning a plate with only a single central aperture, directly above / upstream of the outer region of the multi-aperture array, from which it is possible to perform a measurement based on excess electrons discharged. The embodiment variants as described with respect to the first aspect of the invention can be transferred to the embodiment variant according to the second aspect of the invention. In particular, the absorber layer provided on the pre-aperture plate can be structured in areas that allow measurements over a large area as detailed with respect to the first aspect of the invention. Of course, it is also possible to additionally perform a measurement of excess electrons generated by charged particles impinging on the multi-aperture array. Usually, this will coincide with a measurement in the inner region of the multi-aperture array as described above with respect to the first aspect of the invention. As long as no technical contradiction arises, the embodiment of the present invention according to the first aspect and the embodiment of the present invention according to the second aspect may be combined with each other in whole or in part.

[0051] In this context, the invention will be better understood with reference to the accompanying drawings. [Brief description of the drawings]

[0052] [Figure 1] FIG. 1 is a schematic diagram showing a multi-beam particle microscope (MSEM). [Diagram 2] FIG. 2 shows a schematic diagram of beam current measurement. [Diagram 3] FIG. 2 shows a schematic diagram of a multi-aperture array with an absorbing layer on top. [Figure 4] FIG. 13 shows a comparison between a single beam current and the current generated by excess electrons discharged from the absorbing layer of a multi-aperture array. [Diagram 5] FIG. 13 shows a schematic diagram of another beam current measurement. [Figure 6] FIG. 2 shows a schematic diagram of a quadrant detector; [Figure 7] FIG. 13 shows a schematic diagram of another quadrant detector; [Figure 8] FIG. 13 is a schematic diagram illustrating adjustment of the beam cone of an illumination beam upon incidence on a multi-aperture array. [Figure 9] FIG. 2 is a schematic diagram showing an electrostatic bi-deflector in the region of a focusing lens system. [Figure 10] FIG. 1 shows a schematic diagram of a multi-beam particle microscope having a closed loop beam current control means and a compensator controlled using a controller. [Figure 11] FIG. 2 shows a schematic diagram of details regarding beam current control. [Figure 12] FIG. 13 is a diagram showing schematic details of another beam current control based on X-ray measurement. [Figure 13] FIG. 1 shows a schematic diagram of a beam current measurement means using X-rays that are converted into NIR radiation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0053] FIG. 1 is a schematic diagram of a particle beam system 1 in the form of a multi-beam particle microscope 1 using multiple particle beams. The particle beam system 1 generates multiple particle beams that impinge on an object to be examined in order to generate there interaction products, e.g. secondary electrons, that emanate from the object and are subsequently detected. The particle beam system 1 is of the scanning electron microscope (SEM) type, using multiple primary particle beams 3 that are incident on the surface of the object 7 at multiple positions 5 and generate there multiple electron beam spots, or spots, spatially separated from one another. The object 7 to be examined can be of any desired type, e.g. a semiconductor wafer or a biological sample, and can include an array of microelements or the like. The surface of the object 7 is arranged at a first surface 101 (object surface) of an objective lens 102 of the objective lens system 100.

[0054] Enlarged view I1 of Fig. 1 shows a plan view of an object plane 101 with a square field 103 of 5 incidence positions formed in the first plane 101. In Fig. 1 the number of incidence positions is 25 forming a 5 x 5 field 103. The number of incidence positions 25 is a number chosen for a simplified illustration. In practice the number of beams and therefore the number of incidence positions can be chosen to be significantly larger, for example 20 x 30, 100 x 100, etc.

[0055] In the illustrated embodiment, the field of view 103 of the entrance positions 5 is substantially square with a constant pitch P1 between adjacent entrance positions. Example values ​​of the pitch P1 are 1 micrometer, 10 micrometers and 40 micrometers. However, the field of view 103 can have other symmetric shapes, such as, for example, hexagonal symmetry.

[0056] The diameter of the beam spot formed in the first plane 101 can be very small. Example values ​​of this diameter are 1 nanometer, 5 nanometers, 10 nanometers, 100 nanometers and 200 nanometers. The focusing of the particle beam 3 to form the beam spot 5 is performed by the objective lens system 100.

[0057] Primary particles striking the object generate interaction products, e.g. secondary electrons, backscattered electrons or primary particles whose motion has been reversed for other reasons, emanating from the surface of the object 7 or from the first face 101. The interaction products emanating from the surface of the object 7 are shaped by the objective lens 102 to form a secondary particle beam 9. The particle beam system 1 provides a particle beam path 11 for directing the multiple secondary particle beams 9 to a detector system 200. The detector system 200 includes a particle optical unit with a projection lens 205 for directing the secondary particle beams 9 to a particle multi-detector 209.

[0058] 1 shows a plan view of a surface 211 on which the individual detection areas of the particle multi-detector 209 are located, where the secondary particle beam 9 is incident at positions 213. The incident positions 213 lie within a field of view 217 with a regular pitch P2 from one another. Example values ​​for the pitch P2 are 10 micrometers, 100 micrometers and 200 micrometers.

[0059] The primary particle beam 3 is generated in a beam generator 300 that includes at least one particle source 301 (e.g., an electron source), at least one collimation lens 303, a multi-aperture array 305, and a field lens 307. The particle source 301 generates a diverging particle beam 309, which is collimated or at least substantially collimated by the collimation lens 303 to shape a beam 311 that illuminates the multi-aperture array 305.

[0060] Extract I3 of FIG. 1 shows a plan view of the multi-aperture array 305. The multi-aperture array 305 includes a multi-aperture plate 313 having a plurality of openings or apertures 315 formed therein. Midpoints 317 of the apertures 315 are located within a field of view 319 that is imaged to a field of view 103 formed by the beam spot 5 at the object plane 101. The pitch P3 between the midpoints 318 of the apertures 315 can have example values ​​of 5 micrometers, 100 micrometers and 200 micrometers. The diameter D of the apertures 315 is smaller than the pitch P3 between the midpoints of the apertures. Example values ​​of the diameter D are 0.2×P3, 0.4×P3 and 0.8×P3.

[0061] Particles of the illumination particle beam 311 pass through the aperture 315 and form the particle beam 3. Particles of the illumination beam 311 that strike the plate 313 are absorbed by the plate 313 and do not contribute to the formation of the particle beam 3.

[0062] The applied electrostatic field causes the multi-aperture array 305 to focus each of the particle beams 3 to form a beam focus 323 in the plane 325. Alternatively, the beam focus 323 can be virtual. The diameter of the beam focus 323 can be, for example, 10 nanometers, 100 nanometers, and 1 micrometer.

[0063] The field lens 307 and the objective lens 102 provide a first imaging particle-optical unit for imaging a plane 325 where the beam focus 323 is formed onto a first plane 101, such that a field 103 of incidence positions 5 or beam spots arises thereat. When the surface of the object 7 is arranged in the first plane, a beam spot is correspondingly formed on the objective surface.

[0064] The objective lens 102 and the projection lens arrangement 205 provide a second imaging particle-optical unit for imaging the first plane 101 onto the detection plane 211. The objective lens 102 is therefore a lens that is part of both the first and the second particle-optical units, whereas the field lens 307 belongs only to the first particle-optical unit and the projection lens 205 belongs only to the second particle-optical unit.

[0065] A beam switch 400 is disposed in the beam path of the first particle-optical unit between the multi-aperture array 305 and the objective lens system 100. The beam switch 400 is also part of the second optical unit in the beam path between the objective lens system 100 and the detector system 200.

[0066] Further information regarding such multi-beam particle beam systems and the components used therein, such as, for example, particle sources, multi-aperture plates and lenses, can be taken from International Patent Applications WO2005 / 024881A2, WO2007 / 028595A2, WO2007 / 028596A1, WO2011 / 124352A1 and WO2007 / 060017A2, and German Patent Application Publication Nos. 102013016113 and 102013014976, the disclosures of which are incorporated in their entirety into the present application by reference.

[0067] FIG. 2 shows a schematic representation of the beam current measurement. The multi-aperture array 304 is shown in a cross-sectional view. On its upper side, the multi-aperture array 304 comprises an absorbing layer 341 capable of absorbing charged particles. In the illustrated embodiment, the entire upper side of the multi-aperture array 304 is covered by the absorbing layer 341. In this embodiment, the multi-aperture plate is arranged as a first multi-aperture array downstream of a focusing lens system (not shown in FIG. 2). An illumination particle beam 311 is incident on the multi-aperture array 304. A majority of the incident particles of the illumination particle beam 311 impinge on the absorbing layer 304a, and a small proportion of all particles pass through the aperture 304a, thus giving rise to a plurality of first individual charged particle beams 3. A part of the illumination particle beam 311 impinges on the outer region 366 of the multi-aperture array 304, and as an example, particle beam 311Bb is shown in FIG. 2. Another part of the illumination particle beam 311 impinges on the multi-aperture array 304 in the inner region 367. Some of these particles are shown as an example in FIG. 2 with the reference 311a. In this embodiment, the multi-aperture array 304 is not structured. Every particle that impinges on the absorbing layer 341 therefore gives rise to an excess of electrons that are discharged from the absorbing layer 341 and measured by a first beam current measuring means 370, which in this case is realized as a picoammeter. The measured value is transmitted to the controller 10 and is used for example to control the beam generation system, for example the voltage applied to the extractor electrode, or for control by setting the temperature of the particle source. Other control loops are also possible.

[0068] In the illustrated embodiment, only one picoammeter is applied, positioned between the connection to the absorbing layer 341 and the ground electrode. Thus, the entire area of ​​the absorbing layer 341 contributes to the measurement, which includes the measurement of discharge excess electrons generated by charged particles impinging on the multi-aperture array 304 in the outer region 366 and the inner region 367. The illustrated measurement principle is a measurement over a large area, which ensures a very good signal-to-noise ratio. In the illustrated embodiment, the average single beam current of the plurality of first individual particle beams 3 is less than 1 / 1000 of the total beam current measured by the first current measuring means 370. Please note that the dimensions in FIG. 2 are not to scale.

[0069] Figure 3 shows a schematic representation of a multi-aperture array 304 with an upper absorbing layer 341. Figure 3a shows in top view the multi-aperture array 304 already shown in Figure 2. It should be noted that the absorbing layer 341 is unstructured and the entire surface of the absorbing layer 341 is available for the measurement of excess electrons.

[0070] In contrast, FIG. 3b shows a multi-aperture plate 304 structured in two separate regions separated from each other. The first region is identical to the outer region 366, defined as the region around all of the openings 304a in the multi-aperture array 304. The second region is the inner region 367, which includes all of the openings 304a in the multi-aperture array 304. In the illustrated embodiment, the apertures 304a are arranged in a hexagonal shape. The structuring 368 or separation 368 is therefore also provided as a hexagon. Of course, even if the overall arrangement of the apertures 304a is selected as a hexagon, other shapes of the separation can also be selected. It is also possible, for example, to select a circular shape or, for example, a rectangular shape. It should be noted that also in FIG. 3b, an absorber layer 341 is provided on the entire surface of the multi-aperture array 304, with reference 341a indicating the absorber layer in the outer region 366 and reference 341b indicating the absorber layer in the inner region 367. The absorbent layers in the inner region 367 and the outer region 366 can be selected to be of the same material, but the materials can also be selected to be different. According to one embodiment, the absorbent layer can include or consist of any one of gold, silver, titanium, platinum. As a rule, noble metals are preferred, as they have good electrical conductivity.

[0071] According to the embodiment shown in Fig. 3b, both absorbing layers 341a and 341b can be connected to a ground electrode, respectively. The excess electrons discharged from the absorbing layer 341a are measured in each case by an ammeter 370. In contrast, the measurement of the excess electrons discharged from the absorbing layer 341b by a separate ammeter is optional. It should be noted that there is no further structuring in the inner region 367 of the multi-aperture array 304. Thus, the formation of the multiple first individual particle beams 3 is in no way hindered by the presence of any structuring or electrodes on the multi-aperture array 304.

[0072] In FIG. 4, the single beam current is compared with the current generated by the excess electrons discharged from the absorbing layer 341 of the multi-aperture array 304. The curve indicated by the reference C1 indicates the current measured by the first current measuring means 370. The reference C2 indicates the single beam current (shifted in the graph) measured, for example, by the second beam current measuring means, for example with a Faraday cup temporarily placed on the stage during the calibration of the entire multi-beam particle microscope. An important result of this comparison is that the fluctuations and fluctuations occurring in the single beam current (curve C2) are reflected in the curve C1 as well as in the measurement, which therefore does not aim at measuring the single beam current at all but is in principle an ensemble measurement. This result is a decisive basis for enabling the change of the measurement principle according to the invention. It is no longer the aim to measure as many single beam currents as possible separately by additional detectors arranged separately near each aperture in the multi-aperture array 304. Instead, the goal is a measurement with a very good signal-to-noise ratio, which can be achieved by an ensemble measurement, or more precisely by measuring over a large area on the multi-aperture array 304. As an incidental remark, it is noted that the required proportionality between the single beam current and the measured overall "coating" current cannot be automatically found by large area measurements performed at other apertures in the system. Ensemble measurements made at the extractor aperture or at the aperture of the anode of the particle source did not show the required proportionality between the two parameters.

[0073] FIG. 5 shows a schematic diagram of another beam current measurement according to another embodiment of the invention. In this example, the multi-beam generator includes a pre-aperture plate 380 and a multi-aperture array 304. As before, the entire surface of the multi-aperture array 304 is covered by an absorbing layer 341 connected to ground. However, immediately upstream of the aperture array 304, a pre-aperture plate 380 is provided. Essentially, this pre-aperture plate 380 covers or blocks the outer region 366 of the multi-aperture array 304, giving rise to its own "outer region" 366a. Particles impinging on the pre-aperture plate 380 are absorbed by the absorbing layer 341a and converted into excess electrons, which are discharged from the layer 341a and transported to the ground electrode. In this line to ground, a first beam current measuring means 370 is provided as a single picoammeter. The measurements are transmitted to the controller 10. Again, based on this measurement the controller 10 is configured for example to drive the beam generating system or to control the collecting lens system. Optionally, not shown in Fig. 5, further components of the first beam current measuring means 370 can be arranged in the line from the absorbing layer 341 to ground, so that essentially excess electrons generated by impinging particles on the multi-aperture array 304 in the inner region 367 can also be measured.

[0074] In Fig. 6 a quadrant detector is shown diagrammatically. According to the illustrated embodiment, the multi-aperture plate 304 is structured into five separate regions 351, 352, 353, 354 and 367, which are separated from one another. Each region 351, 352, 353, 354 and 367 is connected to ground. The first beam current measuring means 370 comprises in the illustrated example five components 370a, 370b, 370c, 370d and 370e. In each case the excess electrons are measured and the measurement results are transmitted to the controller 10. It should be noted that the inner region 367 comprises all the openings in the multi-aperture array 304. The inner region 367 is therefore not at all disturbed by any structuring or by a separately provided detector. This ensures a very good beam current quality of the generated individual particle beam 3. The outer region 366 is subdivided into four quadrants 351, 352, 353 and 354. Quadrants 351 and 353 have the same size area. The same applies to the larger areas of regions 352 and 342. If the beam cone of illumination particle beam 311 impinges on the multi-aperture array 304 centrally positioned, the signals generated by measurements in regions 351 and 353 should show the same signal intensity. The same applies to the signals generated by measurements in regions 352 and 354. In a different scenario, when the beam cone of illumination particle beam 311 is shifted in one direction, the signals generated by each quadrant 351, 352, 353 and 354 show a variation that allows to identify the direction of this shift. This shift can be corrected, for example, by controlling a bi-deflector in the area of ​​the focusing lens system that allows a parallel shift of the entire illumination beam cone 311.

[0075] Of course, the quadrant detector shown in Figure 6 can in principle be realised in different ways: the shape of the quadrants can be varied, and therefore also the arrangement of the apertures themselves, which in this example are shown as hexagons.

[0076] In principle, directional variations across the illumination beam cone 311 can already be determined by a detector that includes only the three outer regions. One example is a direction-indicating tripartite detector, where the outer region 366 is subdivided into three different regions, preferably spanning approximately 120 degrees of the outer region.

[0077] Of course, it is also possible to further structure the outer region 366 into more than four separate regions. However, it must be noted that any structuring or separation provided on the multi-aperture array 304 carries a potential risk of beam quality degradation of the first individual particle beams 3, which must be avoided. Also, the larger the area for measurement, the better the achievable signal-to-noise ratio for this type of measurement. The total number of separate regions on the multi-aperture array 304 preferably does not exceed six regions, and preferably only strictly four or five separate, separated regions.

[0078] 6, the excess electrons emanating from the inner region 367 are measured by the first beam current measuring means 370e. However, this measurement is only optional and it is not necessary to provide the first beam current measuring means 370e in all cases. Instead, the central region 367 can be connected only to the ground electrode without any further measurements in between.

[0079] Another quadrant detector is shown diagrammatically in Fig. 7 with regions 355, 356, 357 and 358. In this case too, the whole surface of the multi-aperture plate 304 is provided with an absorbing layer 341. However, the embodiment shown in Fig. 7 has the drawback that in the inner region of the multi-aperture array 304 there is also a structuring / separation which risks an undesirable degradation of the beam quality of the individual charged particle beams 3. Therefore, the illustrated embodiment is less advantageous, even though it meets the requirement of measuring over a large area.

[0080] Fig. 8 shows a schematic diagram of the adjustment of the beam cone of the illumination beam 311 upon incidence on the multi-aperture array 313. The beam current for each individual particle beam 3 can be adjusted by adjusting the beam cone. First, the particles or diverging particle beam 309 are emitted by the source 301. The diverging particle beam 309 passes through a collimation lens system or a condenser lens system 303, which in this embodiment comprises two condenser lenses 303.1 and 303.2. Fig. 8 shows here two different settings of the condenser lens system 303. In the first setting, the condenser lens 303.1 is activated and the condenser lens 303.2 is deactivated. As a result, the particles of the diverging particle beam 309 are collimated in the condenser lens 303.1 and impinge on the multi-aperture array 313 as an illumination particle beam 311.1 with a diameter d1. In the second case, the condenser lens 303.1 is deactivated and the condenser lens 303.2 is activated. The diverging particle beam 309 thus widens further and is collimated only in the second focusing lens 303.1 such that an illuminating particle beam 311.2 with diameter d2 is incident on the multi-aperture plate 313. The number of particles incident on the multi-aperture array 313 is the same in both cases, but the density is different. Thus, when the multi-aperture array 313 with the aperture 315 (not shown) is traversed, individual particle beams 3 are formed with different beam current intensities that depend on the diameter of the illumination spot.

[0081] In the illustrated embodiment, the collector lenses 303.1 and 303.2 are in each case magnetic lenses. However, it is also possible to replace one or both of the magnetic lenses with electrostatic collector lenses. It is also possible to vary the number of collector lenses in the overall collector lens system 303, i.e. to provide only one lens or to provide three or more lenses. Also, one or more deflectors can be provided for the adjustment of the illumination beam 311. These adjustment means and the type of collector lens influence how quickly the illumination spot can be adjusted. This will be explained in more detail below within the scope of this patent application. Firstly, it is illustrated here how different beam currents of the individual particle beams result when different illumination spots are used.

[0082] Further design options for the closed-loop beam current control means are shown in Fig. 9. Fig. 9 shows radiation of a diverging particle beam 309 moving along the optical axis 105 and generated by means of a beam generation system 301. This radiation passes through a collector lens system 33 having a first collector lens 303.1 and a second collector lens 303.2. In the illustrated embodiment, each collector lens is a magnetic lens. An electrostatic bi-deflector with components 345 and 346 is arranged in the region of the collector lens system 303. In the illustrated embodiment, component 345 is downstream of the first collector lens 303.1 and component 346 is downstream of the second collector lens 303.2 with respect to the particle-optical beam path. However, other arrangements of the bi-deflector in the region of the collector lens system 303 are also possible, for example both components 345, 346 can be arranged downstream of the second collector lens 303.2 with respect to the particle-optical beam path.

[0083] The beam 311 can be offset in parallel using a bi-deflector. Upon incidence on the multi-aperture array 313, the beam 311 is offset relative to the optical axis 105 by a vector V. In this case, the electrostatic bi-deflectors 345, 346 can be driven quickly and are suitable for high-frequency correction of the offset when the multi-aperture array 313 is illuminated. Furthermore, the bi-deflectors 345, 346 can be driven based on a current value measured using a first beam current measuring means, for example measured using a sensor 370 at the surface of the multi-aperture plate 313. This feedback loop can also be used for fast closed-loop current control during the image recording procedure.

[0084] Also, one of the collector lenses 303 can be formed as an electrostatic collector lens 303, which can also be rapidly and quasi-instantaneously actuated to result in varying the diameter d of the illumination spot upon incidence on the multi-aperture plate 313. Again, the actuation can be implemented in the form of a feedback loop based on current measurement, determined for example using a sensor 370 above the multi-aperture array 313.

[0085] In Fig. 10, a multi-beam particle microscope 1 with closed-loop beam current control means and compensator, driven by means of a controller 10, is shown diagrammatically. The controller 10 can be formed in one part or in multiple parts, and the entire multi-beam particle microscope 1 can in principle be controlled by means of the controller 10. In particular, the controller 10 controls the beam generation system 301, the components of the first particle-optical unit, the second particle-optical unit and the detection system 200, as well as further components of the multi-beam particle microscope 1, which may or may not be explicitly shown. In the schematic diagram of Fig. 10, only the most important control elements and aspects in the context of the present invention are represented by connecting lines to selected particle-optical components.

[0086] First, the beam current is measured using various beam current measurement means and the measurements are sent to the controller 10. In the illustrated embodiment, a first beam current measurement means configured to at least measure discharge excess electrons generated by charged particles impinging on the multi-aperture array in the outer area around all of the openings in the multi-aperture array can be connected to the micro-optics 306 including the multi-aperture array 313. In this case, this can be, for example, a detection mechanism as shown in Fig. 2, 3, 5, 6 or 7. Furthermore, in the illustrated embodiment, the total beam current is measured using a sensor system arranged on or associated with the beam stop 111. In this case, a multi-beam deflector 390 is used, arranged in the first particle-optical beam path upstream of the objective lens 102 and at the same height as the crossover surface, to steer the individual particle beam 3 on to the beam stop 111. In particular, the controller 10 can be configured to direct the first individual particle beam 3 into the beam stop 111 during a line jump or an image jump when scanning on the sample surface. Thus, the total beam current can be measured during the image recording procedure. Alternatively or additionally, the beam current of the individual particle beams can be measured using a Faraday cup or an array of Faraday cups provided on the sample stage 503 for the calibration process.

[0087] The components of the multi-beam particle microscope 1 are driven in a manner known per se, including the adjustment of the extractor voltage in the beam generation system 301 and the driving of the collecting lens system 303. A deflector 330, additionally shown in Fig. 10, serves to perform a static adjustment of the illumination beam 311 at its entrance into the micro-optical system 306. However, the multi-beam particle microscope 1 can include further components and control elements for low-frequency or high-frequency driving for the purpose of controlling the beam current.

[0088] Additionally or alternatively, the focusing lens of the focusing lens system 303 can be designed as a fast electrostatic focusing lens and can be driven quickly as well, so that the diameter of the beam entering the micro-optical system 306 can be quickly corrected.

[0089] For fast correction of the lateral offset of the illumination spot, one or more electrostatic deflectors, in particular an electrostatic bi-deflector as shown for example in Fig. 8, may additionally or alternatively be provided in the collector lens system 303. These deflectors may also be driven by means of a feedback signal based on the current value measured by means of the first beam current measurement means.

[0090] In Fig. 11, details regarding the beam current control are shown. More specifically, details of the particle source control loop are shown. A current monitoring processor 840 is configured for the control loop. The input signal of the control loop is a measurement made by a first beam current measurement means configured to at least measure discharge excess electrons generated by charged particles impinging on the multi-aperture array 304 in the outer area around all of the apertures in the multi-aperture array 304. The first beam current measurement means, which can be realized by an ammeter, in particular a picoammeter, is not shown in Fig. 11. However, an absorber layer 341 provided on the upper side of the multi-aperture array 304 is shown in schematic form. The multi-aperture array 304 is part of a multi-aperture arrangement 305, which further includes a second multi-aperture 306 plate, which can include, for example, a lens array, a deflector array and / or an astigmatism corrector array, and a final multi-aperture plate 310. Other configurations are possible.

[0091] The current monitoring processor 840 is part of the overall controller 10 of the multi-beam particle microscope 1. The current monitoring processor 840 is configured to control the beam generating system 301 and / or the collection lens system 303 based on measurements using the first beam current measuring means 370. Other particle-optical components may also be controlled.

[0092] The beam generating system 301 includes several parts. In the illustrated embodiment, the beam generating system 301 includes a particle source tip 301.1, a suppressor electrode 301.2 and an extractor electrode 301.3. The current monitoring processor 840 can be configured to control the beam generating device 301, for example, by setting a voltage supplied to the extractor electrode 301.3. Additionally or in addition, the controller 840 can be configured to control the beam generating device 301 by setting a temperature of the particle source 301.1, in particular by setting a heating current or a heating voltage. Additionally or alternatively, the voltage supplied to the suppressor electrode 301.2 can be set.

[0093] Additionally or alternatively, the controller 840 can control a collecting lens system 303, which in this case comprises three collecting lenses 303.a, 303.b and 303.c, which are controllable to set the focal length and also to set the diameter of the illumination particle beam 311 impinging on the multi-aperture array 304, more precisely on the first multi-aperture array 304 in the illustrated embodiment.

[0094] In the embodiment shown, a bi-deflector 303.d, in particular an electrostatic bi-deflector 303.d, is provided in the region of the collector lens system 303. The controller 840 is configured to control the bi-deflector 303.d based on measurements using the first beam current measuring means 370.

[0095] Optionally, the controller 840 may also control the electrodes 307.1 which generate the immersion field in the first multi-aperture array 304. Optionally, a controlled multi-pole electrode for tilt correction may also be provided, controllable by the controller 840.

[0096] According to the above described embodiments, the controlled variable in each case is the current generated by discharge excess electrons, which are generated by charged particles impinging on the multi-aperture array 304 in the outer region 366 around all of the openings in the multi-aperture array 304. However, it is also possible to use another controlled variable other than the current generated by discharge excess electrons, and according to an alternative solution, the controlled variable is x-ray detection.

[0097] FIG. 12 shows in schematic form another detail of the beam current control based on the measurement of X-rays 900. In the illustrated embodiment, an X-ray detector 950 is provided instead of a current meter measuring discharge excess electrons. The X-rays 900 are generated by charged particles impinging on the upper absorbing layer 341 of the multi-aperture array 304. Experiments carried out by the inventors have shown that the amount of X-rays or the number of X-ray photons measured by the X-ray detector 950 is proportional to the beam current of the first individual particle beam impinging on the sample at the incidence position. In this case, the X-ray detector 950 is provided as a ring-shaped scintillator element on the outer periphery of the multi-aperture array 304. With this configuration, a good signal-to-noise ratio can be achieved. The controller 840 is in this case configured to control the beam generation system 301 based on the measurement with the X-ray detector 950. The remaining elements of the current control by X-ray detection are the same as those already shown and described in detail in FIG. 11, and the same reference numbers indicate the same elements. To avoid unnecessary repetition, please refer to FIG. 11 for further explanation.

[0098] Fig. 13 shows a schematic representation of another realization of a beam current measurement means using X-rays 900 converted into NIR (near infrared) radiation. In the illustrated embodiment, the multi-aperture array 304 includes a quartz plate 905 coated with an absorbing layer 341. Instead of the quartz plate 905, other plates of transparent material, such as PMMA, can be used. The quartz plate is doped with a fluorescent agent that acts as a scintillator. Charged particles, such as electrons, that impinge on the absorbing layer 341 are first converted into X-rays 900. In the quartz plate 905, the X-rays 900 are converted into photons or near infrared radiation 901. The photons 901 are guided by internal reflection in the quartz plate 905 and are finally detected by one or more photodetectors 910 arranged on the outer periphery of the quartz plate 905. By way of example, a point T at which total reflection of the photons 901 occurs is illustrated in Fig. 13. Signals measured by the one or more photodetectors 910 are communicated to the controller 10 (or for example a component 840 thereof) and used to control the beam generating system 301 and / or the collecting lens system 303. Other types of control than those shown diagrammatically in Figure 12 can also be performed. In this regard, see Figure 12 and also Figure 11.

[0099] Also, according to this embodiment, the required proportionality between the beam current of the individual particle beams impinging on the sample and the near infrared radiation detected using the photodetector 910 exhibits the required proportionality.

[0100] A multi-beam particle microscope with improved beam current control is disclosed. Excess electrons discharged from one or only a few regions of an absorber layer provided on a multi-aperture array are measured using an ammeter. The measured current is used as a controlled variable in a closed-loop control. The measurement is large-area and low-noise. The multi-aperture array can be specially structured to also provide direction-sensitive detection, for example using a quadrant or tripartite detector.

[0101] Example 1 1. A multi-beam particle microscope, comprising: a beam generating system configured to generate a first charged particle beam, the beam generating system including a particle source, an extractor electrode, and an anode; a multi-beam generator having a multi-aperture array configured to generate a first field of a plurality of first individual charged particle beams from a first charged particle beam, the multi-aperture array including an absorber layer thereon for absorbing the charged particles, the absorber layer being connected to at least one ground electrode for discharging excess electrons; an x-ray detector configured to detect x-rays generated by charged particles impinging on an absorbing layer of the multi-aperture array; a first particle-optical unit having a first particle-optical beam path configured to direct the generated first individual particle beam towards the sample such that the first individual particle beam strikes the sample at an incidence position forming a second field of view; A detection system; a second particle-optical unit having a second particle-optical beam path configured to image a second individual particle beam emanating from an incidence position within the second field of view onto the detection system; a particle-optical objective lens through which both the first and second individual particle beams pass; a beam switch disposed in the first particle-optical beam path between the multi-beam particle source and the objective lens and disposed in the second particle-optical beam path between the objective lens and the detection system; a controller configured to control the beam generation system, the particle-optical objective, the first particle-optical unit, the second particle-optical unit, and the detection system; a controller configured to drive the beam generating system based on measurements using the X-ray detector; and / or A multi-beam particle microscope, wherein the controller is configured to control the focusing lens system based on measurements using the x-ray detector.

[0102] Example 2 2. A multi-beam particle microscope as described in Example 1, wherein the X-ray detector is provided as a ring-shaped scintillator element upstream of and around the periphery of the multi-aperture array.

[0103] Example 3 a beam generating system configured to generate a first charged particle beam, the beam generating system including a particle source, an extractor electrode, and an anode; a multi-beam generator having a multi-aperture array configured to generate a first field of a plurality of first individual charged particle beams from a first charged particle beam, the multi-aperture array including an absorber layer thereon for absorbing the charged particles, the absorber layer being connected to at least one ground electrode for discharging excess electrons; an x-ray conversion means for converting x-rays generated by charged particles impinging on the absorbing layer of the multi-aperture array into NIR radiation; a light guide for directing the NIR radiation to a photodetector; a photodetector configured to detect NIR radiation; a first particle-optical unit having a first particle-optical beam path configured to direct the generated first individual particle beam towards the sample such that the first individual particle beam strikes the sample at an incidence position forming a second field of view; A detection system; a second particle-optical unit having a second particle-optical beam path configured to image a second individual particle beam emanating from an incidence position within the second field of view onto the detection system; a particle-optical objective lens through which both the first and second individual particle beams pass; a beam switch disposed in the first particle-optical beam path between the multi-beam particle source and the objective lens and disposed in the second particle-optical beam path between the objective lens and the detection system; a controller configured to control the beam generation system, the particle-optical objective, the first particle-optical unit, the second particle-optical unit, and the detection system; a controller configured to drive the beam generating system based on measurements using the photodetector; and / or A multi-beam particle microscope, wherein the controller is configured to control the collection lens system based on measurements using the photodetector.

[0104] Example 4 the light guide includes a quartz glass plate doped with a scintillating material for converting x-rays to NIR radiation; A multibeam particle microscope as described in Example 3, in which the photodetectors are arranged around the periphery of the quartz glass plate. [Explanation of symbols]

[0105] 1. Multibeam Particle Microscope 3 Primary particle beam (individual particle beam) 5 Beam spot, incident position 7 Object 9 Secondary particle beam 10 Computer system, controller 11 Secondary particle beam path 13 Primary Particle Beam Path 25 Sample surface, wafer surface 100 Objective Lens System 101 Objective surface 102 Objective Lens 103 Field of view 105 Optical axis of multi-beam particle microscope 108 Crossover 110 Batch scanning deflector 111 Beam stop equipped with second current measuring means 200 detector system 205 Projection Lens 207 Detection Area 208 Adjustment deflector 209 Particle Multi-Detector 211 Detection surface 212 Crossover 213 Incident position 214 Aperture Filter 215 Detection Area 216 Active Elements 217 Field of view 218 Deflector System 220 Multi-aperture corrector, individual deflector array 222 Collective deflection system, anti-scan 300 Beam Generator 301 Particle source, beam generation system 303 Collimation Lens System 304 Multi-Aperture Array 304a aperture 305 Multi-Aperture Array 306 Micro-optical system 307 Field of view lens 308 Field of view lens 309 Diverging Particle Beam 311 Radiation Particle Beam 313 Multi-aperture plate, multi-aperture array 315 Multi-aperture plate aperture 316 hexagon 317 Midpoint of Opening 319 Field of view 323 Beam Focus 325 Intermediate image plane 326 Field of View Lens System 330 Deflector 340 Tip 341 Absorbing Layer 342 Extractor Electrode 343 Anode 345 Deflector 346 Deflector 351 areas 352 areas 353 areas 354 areas 360 Beam current intensity diagram 366 outer area 367 Inner area 368 Structuring, separation 370 First beam current measuring means, ammeter, picoammeter 380 Pre-aperture plate 390 Multi-beam deflector 400 Beam Switch 420 Magnetic Elements 500 Sample Stage 503 Sample voltage source 900 X-ray 901 photons, NIR radiation 905 Crystal plate 910 Photodetector 950 X-ray detector d1 Beam cone diameter d2 Beam cone diameter Misalignment between the midpoint of the V-beam cone and the midpoint of the multi-aperture array T total reflection point

Claims

1. 1. A multi-beam particle microscope, comprising: a beam generating system configured to generate a first charged particle beam, the beam generating system including a particle source, an extractor electrode, and an anode; a multi-beam generator having a multi-aperture array configured to generate a first field of a plurality of first individual charged particle beams from the first charged particle beam, the multi-aperture array including an absorber layer on an upper side thereof for absorbing charged particles, the absorber layer being connected to at least one ground electrode for discharging excess electrons; a first beam current measuring means configured to measure at least discharge excess electrons generated by charged particles impinging on the multi-aperture array in an outer region around all of the apertures in the multi-aperture array; a focusing lens system disposed between the beam generating system and the multi-beam generator; a first particle-optical unit having a first particle-optical beam path configured to direct a generated first individual particle beam towards the sample such that the first individual particle beam strikes the sample at an incidence position forming a second field of view; A detection system; a second particle-optical unit having a second particle-optical beam path configured to image a second individual particle beam emanating from the entrance position within the second field of view onto the detection system; a particle-optical objective lens through which both the first and second individual particle beams pass; a beam switch disposed in the first particle-optical beam path between the multi-beam generator and the objective lens, and disposed in the second particle-optical beam path between the objective lens and the detection system; a controller configured to control the beam generation system, the focusing lens system, the particle-optical objective, the first particle-optical unit, the second particle-optical unit, and the detection system; the controller is configured to control the beam generating system based on measurements using the first beam current measurement means; and / or the controller is configured to control the collection lens system based on measurements using the first beam current measurement means; the absorbing layer is structured in an inner region that includes the openings of the multi-aperture array and in an outer region all around the openings in the multi-aperture array; the outer region is further structured into four separate regions arranged to form a direction indicating quadrant detector; the four separate regions of the inner region and the outer region being isolated from each other and connected to ground; the first beam current measuring means is configured to measure the excess electrons discharged from each quadrant separately over a large area; Multibeam particle microscope.

2. A multi-beam particle microscope, comprising: a beam generating system configured to generate a first charged particle beam, the beam generating system including a particle source, an extractor electrode, and an anode; a multi-beam generator having a multi-aperture array configured to generate a first field of a plurality of first individual charged particle beams from the first charged particle beam, the multi-aperture array including an absorber layer on an upper side thereof for absorbing charged particles, the absorber layer being connected to at least one ground electrode for discharging excess electrons; a first beam current measuring means configured to measure at least discharge excess electrons generated by charged particles impinging on the multi-aperture array in an outer region around all of the apertures in the multi-aperture array; a focusing lens system disposed between the beam generating system and the multi-beam generator; a first particle-optical unit having a first particle-optical beam path configured to direct a generated first individual particle beam towards the sample such that the first individual particle beam strikes the sample at an incidence position forming a second field of view; A detection system; a second particle-optical unit having a second particle-optical beam path configured to image a second individual particle beam emanating from the entrance position within the second field of view onto the detection system; a particle-optical objective lens through which both the first and second individual particle beams pass; a beam switch disposed in the first particle-optical beam path between the multi-beam generator and the objective lens, and disposed in the second particle-optical beam path between the objective lens and the detection system; a controller configured to control the beam generation system, the focusing lens system, the particle-optical objective, the first particle-optical unit, the second particle-optical unit, and the detection system; the controller is configured to control the beam generating system based on measurements using the first beam current measurement means; and / or the controller is configured to control the collection lens system based on measurements using the first beam current measurement means; the absorbent layer is structured into the inner region and the outer region; the outer region is further structured into three separate regions arranged to form a direction indicating tripartite detector; the three separate regions of the inner region and the outer region being isolated from one another and connected to ground; the first beam current measuring means is configured to measure the excess electrons discharged from each of the three divided regions separately. Multibeam particle microscope.

3. 3. The multi-beam particle microscope according to claim 1, wherein the first beam current measuring means is configured to also measure the discharge excess electrons generated by charged particles impinging on the multi-aperture array in an inner region including an aperture in the multi-aperture array.

4. further comprising a bi-deflector in the region of the focusing lens system; 3. A multi-beam particle microscope according to claim 1 or 2, wherein the controller is further configured to control the dual deflector based on measurements using the first beam current measuring means.

5. 3. A multibeam particle microscope according to claim 1 or 2, wherein the first beam current measuring means comprises at least one ammeter, in particular a picoammeter.

6. 3. A multi-beam particle microscope according to claim 1 or 2, wherein at least 60% of the beam current reaching the multi-aperture array is used for the beam current measurement.

7. 3. A multibeam particle microscope according to claim 1 or 2, wherein at least 90%, in particular at least 95%, of the beam current reaching the multi-aperture array is used for the beam current measurement.

8. 3. A multibeam particle microscope according to claim 1 or 2, wherein the active beam measurement surface of the absorbing layer, which absorbs charged particles and emits electrons therefrom for measuring the beam current, is at least 60% of the total surface of the multi-aperture array.

9. 3. A multibeam particle microscope according to claim 1 or 2, wherein the active beam measurement surface of the absorber layer, which absorbs charged particles and emits electrons therefrom for measuring the beam current, is at least 90%, in particular 95%, of the total surface of the multi-aperture array.

10. 3. The multi-beam particle microscope according to claim 1 or 2, wherein the average single beam current of the plurality of first individual particle beams is at least 1 / 100 or less, in particular 1 / 500 or 1 / 1000 or less, of the total beam current measured by the first beam current measuring means.

11. the absorbent layer is an absorbent coating; and / or 3. A multi-beam particle microscope according to claim 1 or 2, wherein the absorbing layer comprises or consists of any one of the following: gold, silver, titanium, platinum.

12. 3. The multi-beam particle microscope of claim 1, wherein the multi-aperture array is arranged as a first multi-aperture array downstream of the focusing lens system, the array splitting the first charged particle beam into the plurality of first individual particle beams.

13. 3. A multi-beam particle microscope according to claim 1 or 2, wherein the multi-aperture array is not arranged as a first multi-aperture array downstream of the focusing lens system.

14. 3. A multi-beam particle microscope according to claim 1 or 2, wherein the controller is configured to control the beam generating device by setting a voltage supplied to the extractor electrode.

15. 3. The multi-beam particle microscope according to claim 1 or 2, wherein the controller is configured for controlling the beam-generating device by setting a temperature of the particle source, in particular by setting a heating current or a heating voltage.

16. A multi-beam particle microscope, comprising: a beam generating system configured to generate a first charged particle beam, the beam generating system including a particle source, an extractor electrode, and an anode; a multi-beam generator having a multi-aperture array configured to generate a first field of a plurality of first individual charged particle beams from the first charged particle beam, the multi-aperture array including an absorber layer on an upper side thereof for absorbing charged particles, the absorber layer being connected to at least one ground electrode for discharging excess electrons; a first beam current measuring means configured to measure at least discharge excess electrons generated by charged particles impinging on the multi-aperture array in an outer region around all of the apertures in the multi-aperture array; a focusing lens system disposed between the beam generating system and the multi-beam generator; a first particle-optical unit having a first particle-optical beam path configured to direct a generated first individual particle beam towards the sample such that the first individual particle beam strikes the sample at an incidence position forming a second field of view; A detection system; a second particle-optical unit having a second particle-optical beam path configured to image a second individual particle beam emanating from the entrance position within the second field of view onto the detection system; a particle-optical objective lens through which both the first and second individual particle beams pass; a beam switch disposed in the first particle-optical beam path between the multi-beam generator and the objective lens, and disposed in the second particle-optical beam path between the objective lens and the detection system; a controller configured to control the beam generation system, the focusing lens system, the particle-optical objective, the first particle-optical unit, the second particle-optical unit, and the detection system; the controller is configured to control the beam generating system based on measurements using the first beam current measurement means; and / or the controller is configured to control the collection lens system based on measurements using the first beam current measurement means; the absorbing layer on the multi-aperture array is structured into exactly two separate regions separated from each other, each region being connected to ground; a first region being an inner region including the apertures of the multi-aperture array, and a second region being the outer region all around the apertures in the multi-aperture array; the first beam current measuring means is configured to measure only the excess charged particles discharged from the outer region. Multibeam particle microscope.

17. The optical system according to claim 1, further comprising a bi-deflector within the region of the focusing lens system; 17. The multi-beam particle microscope of claim 16, wherein the controller is further configured to control the dual deflector based on measurements using the first beam current measuring means.

18. A multi-beam particle microscope as described in claim 16, wherein at least 90%, in particular at least 95%, of the beam current reaching the multi-aperture array is used for the beam current measurement.

19. A multi-beam particle microscope as described in claim 16, wherein the average single beam current of the plurality of first individual particle beams is at least 1 / 100 or less, in particular 1 / 500 or 1 / 1000 or less, of the total beam current measured by the first beam current measuring means.

20. 1. A multi-beam particle microscope, comprising: a beam generating system configured to generate a first charged particle beam, the beam generating system including a particle source, an extractor electrode, and an anode; a multi-beam generator having a pre-aperture plate and a multi-aperture array, the multi-beam generator configured to generate a first field of a plurality of first individual charged particle beams from the first charged particle beam, the multi-aperture array being disposed downstream and proximate to the pre-aperture plate, the multi-aperture array including an absorption layer on an upper side thereof for absorbing charged particles, the absorption layer being connected to at least one ground electrode for discharging excess electrons, the pre-aperture plate including a pre-aperture plate absorption layer on an upper side thereof for absorbing charged particles, the pre-aperture plate absorption layer being connected to at least one ground electrode for discharging excess electrons; a first beam current measuring means configured to measure at least discharge excess electrons generated by charged particles impinging on the pre-aperture plate; a focusing lens system disposed between the beam generating system and the multi-beam generator; a first particle-optical unit having a first particle-optical beam path configured to direct a generated first individual particle beam towards the sample such that the first individual particle beam strikes the sample at an incidence position forming a second field of view; A detection system; a second particle-optical unit having a second particle-optical beam path configured to image a second individual particle beam emanating from the entrance position within the second field of view onto the detection system; a particle-optical objective lens through which both the first and second individual particle beams pass; a beam switch disposed in the first particle-optical beam path between the multi-beam particle source and the objective lens, and disposed in the second particle-optical beam path between the objective lens and the detection system; a controller configured to control the beam generation system, the particle-optical objective, the first particle-optical unit, the second particle-optical unit, and the detection system; the controller is configured to drive the beam generating system based on measurements using the first beam current measuring means; and / or the controller is configured to control the collection lens system based on measurements using the first beam current measurement means; the first beam current measuring means is configured to measure only the excess charged particles discharged from the pre-aperture plate; Multibeam particle microscope.

21. A multi-beam particle microscope, comprising: a beam generating system configured to generate a first charged particle beam, the beam generating system including a particle source, an extractor electrode, and an anode; a multi-beam generator having a pre-aperture plate and a multi-aperture array, the multi-beam generator configured to generate a first field of a plurality of first individual charged particle beams from the first charged particle beam, the multi-aperture array being disposed downstream and proximate to the pre-aperture plate, the multi-aperture array including an absorption layer on an upper side thereof for absorbing charged particles, the absorption layer being connected to at least one ground electrode for discharging excess electrons, the pre-aperture plate including a pre-aperture plate absorption layer on an upper side thereof for absorbing charged particles, the pre-aperture plate absorption layer being connected to at least one ground electrode for discharging excess electrons; a first beam current measuring means configured to measure at least discharge excess electrons generated by charged particles impinging on the pre-aperture plate; a focusing lens system disposed between the beam generating system and the multi-beam generator; a first particle-optical unit having a first particle-optical beam path configured to direct a generated first individual particle beam towards the sample such that the first individual particle beam strikes the sample at an incidence position forming a second field of view; A detection system; a second particle-optical unit having a second particle-optical beam path configured to image a second individual particle beam emanating from the entrance position within the second field of view onto the detection system; a particle-optical objective lens through which both the first and second individual particle beams pass; a beam switch disposed in the first particle-optical beam path between the multi-beam particle source and the objective lens, and disposed in the second particle-optical beam path between the objective lens and the detection system; a controller configured to control the beam generation system, the particle-optical objective, the first particle-optical unit, the second particle-optical unit, and the detection system; the controller is configured to drive the beam generating system based on measurements using the first beam current measuring means; and / or the controller is configured to control the collection lens system based on measurements using the first beam current measurement means; the pre-aperture plate is further structured into four separate regions arranged to form a direction indicating quadrant detector; the four separate regions of the pre-aperture plate being isolated from one another and connected to ground; the first beam current measuring means is configured to measure the excess electrons discharged from each quadrant separately over a large area; Multibeam particle microscope.

22. further comprising a bi-deflector in the region of the focusing lens system; 22. A multi-beam particle microscope according to claim 20 or 21, wherein the controller is further configured to control the dual deflector based on measurements using the first beam current measuring means.

23. A multi-beam particle microscope, comprising: a beam generating system configured to generate a first charged particle beam, the beam generating system including a particle source, an extractor electrode, and an anode; a multi-beam generator having a pre-aperture plate and a multi-aperture array, the multi-beam generator configured to generate a first field of a plurality of first individual charged particle beams from the first charged particle beam, the multi-aperture array being disposed downstream and proximate to the pre-aperture plate, the multi-aperture array including an absorption layer on an upper side thereof for absorbing charged particles, the absorption layer being connected to at least one ground electrode for discharging excess electrons, the pre-aperture plate including a pre-aperture plate absorption layer on an upper side thereof for absorbing charged particles, the pre-aperture plate absorption layer being connected to at least one ground electrode for discharging excess electrons; a first beam current measuring means configured to measure at least discharge excess electrons generated by charged particles impinging on the pre-aperture plate; a focusing lens system disposed between the beam generating system and the multi-beam generator; a first particle-optical unit having a first particle-optical beam path configured to direct a generated first individual particle beam towards the sample such that the first individual particle beam strikes the sample at an incidence position forming a second field of view; A detection system; a second particle-optical unit having a second particle-optical beam path configured to image a second individual particle beam emanating from the entrance position within the second field of view onto the detection system; a particle-optical objective lens through which both the first and second individual particle beams pass; a beam switch disposed in the first particle-optical beam path between the multi-beam particle source and the objective lens, and disposed in the second particle-optical beam path between the objective lens and the detection system; a controller configured to control the beam generation system, the particle-optical objective, the first particle-optical unit, the second particle-optical unit, and the detection system; the controller is configured to drive the beam generating system based on measurements using the first beam current measuring means; and / or the controller is configured to control the collection lens system based on measurements using the first beam current measurement means; the pre-aperture plate is further structured into three separate regions arranged to form a direction indicating quadrant detector; the three separate regions of the pre-aperture plate are isolated from one another and connected to ground; the first beam current measuring means is configured to measure the excess electrons discharged from each of the three divided regions separately. Multibeam particle microscope.

24. The optical system according to claim 23, further comprising a bi-deflector within the region of the focusing lens system; 24. The multi-beam particle microscope of claim 23, wherein the controller is further configured to control the dual deflector based on measurements using the first beam current measuring means.

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